1. Field of the Invention
The present invention relates to a liquid crystal display and a fabrication method thereof and, particularly, to a semi-transmission type liquid crystal display and a fabrication method thereof.
2. Description of the Prior Art
Since liquid crystal itself cannot emit light, a backlight is used in a conventional liquid crystal display. That is, a backlight is arranged behind a liquid crystal panel composed of two transparent substrates and a liquid crystal layer sealed therebetween and characters or picture is displayed on a surface of the liquid crystal panel by allowing a portion of light from the backlight to pass through the panel and blocking another portion of the light. The liquid crystal display of this type is generally referred to as the transmission type liquid crystal display.
In such transmission type liquid crystal display, a fluorescent tube or a LED is used as a light source of the backlight, which consumes electric power. In order to solve the problem of power consumption, a reflection type liquid crystal display has been proposed for use in a battery-powered equipment such as portable equipment, which has no backlight and in which external light incident on a surface of the liquid crystal panel is reflected by a reflector.
Such reflection type liquid crystal display is advantageous in reduction of power consumption due to absence of the backlight. However, the reflection type liquid crystal display cannot be used without external light. That is, in a case where ambient light is dark, intensity of light reflected by the reflector is not enough and so visibility is lowered.
In order to complement the defects of the transmission type liquid crystal display and the reflection type liquid crystal display, JP 2001-75091 A proposes a semi-transmission type liquid crystal display in which a portion of external light is reflected and a portion of light from a backlight is allowed to pass through the liquid crystal display. In the proposed technique, a transparent insulating layer having irregular structure is formed as an underlying layer of pixel electrodes, a transparent electrode is formed on a whole surface of the irregular insulating layer and aluminum reflection electrodes are selectively vapor-deposited on the transparent electrode. Particularly, it is proposed in JP 2001-75091 A that the reflection electrodes are vapor-deposited in not flat regions but irregular regions of the irregular transparent electrode, such that the flat regions of the transparent electrode become light transmitting regions.
It should be noted that very high technique is required in selectively vapor-depositing the reflection electrodes. In addition to this difficulty, highly precise positioning technique is required. Therefore, an application of the proposed technique to a mass production is difficult.
Although, instead of the selective vapor-deposition, a method suitable for mass production may be considered, in which a reflection electrode is vapor-deposited on a whole surface of a transparent electrode and then opening portions are selectively formed therein by etching, the highly precise positioning technique is still required even in such case.
A new problem of the etching processing is that, since developer for removing a photo resist in a patterning step acts as electrolytic agent, battery reaction occurs between aluminum forming the reflection electrode and indium tin oxide (ITO) forming the transparent electrode. That is, since defect of an aluminum film such as pin hole, which is left in the aluminum film when the latter is formed on the transparent electrode by vapor-deposition, is unavoidable in the current technology, battery reaction occurs between the aluminum film and the transparent electrode if the developer enters into the pin hole, so that electrolytic corrosion of not only the aluminum film but also the transparent electrode occurs, causing production yield of the liquid crystal display to be lowered.